Systems and methods for dopant activation using pre-amorphization implantation and microwave radiation

ABSTRACT

Systems and methods are provided for dopant activation in a semiconductor structure for fabricating semiconductor devices. For example, a substrate is provided. A semiconductor structure is formed on the substrate. Pre-amorphization implantation is performed on the semiconductor structure. Microwave radiation is applied to the semiconductor structure to activate dopants in the semiconductor structure for fabricating semiconductor devices. Microwave-radiation absorption of the semiconductor structure is increased after the pre-amorphization implantation.

FIELD

The technology described in this patent document relates generally tosemiconductor materials and more particularly to processing ofsemiconductor materials.

BACKGROUND

Modern semiconductor devices are often fabricated through manyprocesses. As an example, fabricating a field effect transistor usuallyinvolves doping a semiconductor substrate (e.g., adding desiredimpurities into the substrate) to form source/drain junctions. Manydifferent approaches may be implemented for doping the substrate, suchas ion implantation and epitaxial growth. The dopants introduced intothe substrate are usually electrically activated before semiconductordevices can be fabricated on the substrate. The activation of thedopants often includes transferring the dopant atoms/molecules frominterstitial positions into lattice sites of the lattice structure ofthe substrate. Different annealing techniques may be used for dopantactivation, such as low-temperature annealing, rapid thermal annealing(RTA), millisecond thermal annealing (MSA), spike annealing, and laserthermal annealing.

Under certain circumstances, the fabrication process of semiconductordevices involves microwave radiation which typically includeselectromagnetic waves with wavelengths ranging from 1 m to 1 mm(corresponding to frequencies between 0.3 and 300 GHz). When microwaveradiation is applied to a certain material (e.g., a dielectric material)which includes electric dipoles, the dipoles change their orientationsin response to the changing electric fields of the microwave radiationand thus the material may absorb the microwave radiation to generateheat. The response of the material to the electric field of themicrowave radiation can be measured using a complex permittivity, ∈(Ω)*,which depends on the frequency of the electric field:∈(Ω)*=∈(Ω)′−i∈(Ω)″=∈₀(∈_(r)(Ω)′−∈i∈ _(r)(Ω)″)  (1)where Ω represents the frequency of the electric field, ∈(Ω)′ representsa real component of the complex permittivity (i.e., a dielectricconstant), and ∈(Ω)″ represents a dielectric loss factor. In addition,∈₀ represents the permittivity of a vacuum, ∈_(r)(Ω)′ represents therelative dielectric constant, and ∈_(r)(Ω)″ represents the relativedielectric loss factor.

Whether a material can absorb the microwave radiation can becharacterized using a loss tangent, tan δ:

$\begin{matrix}{{\tan\mspace{11mu}\delta} = \frac{{ɛ^{''}\mu^{\prime}} - {ɛ^{\prime}\mu^{''}}}{{ɛ^{\prime}\mu^{\prime}} + {ɛ^{''}\mu^{''}}}} & (2)\end{matrix}$where μ′ represents a real component of the magnetic permeability of thematerial, and μ″ represents a magnetic loss factor. Assuming negligiblemagnetic loss (i.e., μ″=0), the loss tangent of a material is expressedas follows:

$\begin{matrix}{{\tan\mspace{11mu}\delta} = {\frac{ɛ^{''}}{ɛ^{\prime}} = \frac{ɛ_{r}^{''}}{ɛ_{r}^{\prime}}}} & (3)\end{matrix}$

Materials with a low loss tangent (e.g., tan δ<0.01) allow microwaves topass through with very little absorption. Materials with an extremelyhigh loss tangent (e.g., tan δ>10) reflect microwaves with littleabsorption. Materials with an intermediate loss tangent (e.g., 10≧tanδ≧0.01) can absorb microwave radiation.

SUMMARY

In accordance with the teachings described herein, systems and methodsare provided for dopant activation in a semiconductor structure forfabricating semiconductor devices. For example, a substrate is provided.A semiconductor structure is formed on the substrate. Pre-amorphizationimplantation is performed on the semiconductor structure. Microwaveradiation is applied to the semiconductor structure to activate dopantsin the semiconductor structure for fabricating semiconductor devices.Microwave-radiation absorption of the semiconductor structure isincreased after the pre-amorphization implantation.

In one embodiment, an article for fabricating semiconductor devicesincludes a substrate, a semiconductor structure formed on the substrate,and a pre-amorphization layer formed on the semiconductor structurethrough pre-amorphization implantation. Microwave-radiation absorptionof the semiconductor structure being increased after thepre-amorphization implantation. Dopants in the semiconductor structureare activated by applying microwave radiation to the semiconductorstructure for fabricating semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-FIG. 1C depict example diagrams for dopant activation of asemiconductor structure using pre-amorphization implantation andmicrowave-radiation annealing.

FIG. 2 depicts an example diagram for dopant activation using microwaveradiation.

FIG. 3 depicts an example flow chart for dopant activation of asemiconductor structure using pre-amorphization implantation andmicrowave-radiation annealing.

DETAILED DESCRIPTION

The conventional technology for dopant activation often involves highprocessing temperatures. For example, RTA is usually performed at atemperature higher than 950° C., and MSA at a temperature higher than1050° C. Such high processing temperatures may not be suitable for somemodern semiconductor devices.

Microwave radiation may be implemented for dopant activation withoutrequiring a high processing temperature. However, certain semiconductorstructures may have low microwave radiation absorption, and thuseffective dopant activation may not be easy to achieve using microwaveradiation. For example, an epitaxially-grown junction may have a smallnumber of defects which often leads to insufficient dipole formationwithin the junction to interact with the microwave radiation for dopantactivation. Pre-amorphization implantation (PAI) may be performed on asemiconductor structure (e.g., an epitaxially-grown junction) toincrease microwave-radiation absorption of the semiconductor structurefor dopant activation using microwave radiation.

FIG. 1A-FIG. 1C depict example diagrams for dopant activation of asemiconductor structure using pre-amorphization implantation andmicrowave-radiation annealing. As shown in FIG. 1A, the semiconductorstructure 102 may be formed on a substrate 106 and include one or moreregions to be doped for fabrication of semiconductor devices. Forexample, a region 104 corresponds to a source/drain region of atransistor.

Before dopants are introduced into the semiconductor structure 102(e.g., into the region 104), PAI may be performed, e.g., using a plasmadoping technique, to inject certain implantation species 108 (e.g.,ions) into the semiconductor structure 102 (e.g., into the region 104).In response, a pre-amorphization layer 110 may be formed in thesemiconductor structure 102 (e.g., in the region 104), as shown in FIG.1B. For example, the pre-amorphization layer 110 may contain a largeamount of defects as a result of the implantation. As an example, thepre-amorphization layer 110 includes an amorphous layer of a thicknessin a range of about 5 nm to about 15 nm.

In one embodiment, the PAI may be performed across the entire wafer. Inanother embodiment, the PAI may be performed over a portion of the waferby using lithography to mask device regions under which the PAI may notbe desired. As an example, the implantation species 108 may includeboron-based materials (e.g., B₂H₆), silicon-based materials,phosphorous-based materials, arsenic-based materials, antinomy-basedmaterials, germanium-based materials, helium, xenon, argon, or acombination thereof. For example, the semiconductor structure 102 may beformed at an elevated temperature by epitaxial growth, for example,through chemical vapor deposition (CVD).

In some embodiments, a dielectric layer (e.g., an oxide layer) may beformed (e.g., through thermal growth or deposition) on the semiconductorstructure 102 before the PAI is performed. The dielectric layer mayserve to protect the surface of the semiconductor structure 102 toprevent excess implant damage, and/or serve to prevent the implantspecies 108 from scattering in a horizontal direction.

After the PAI process, dopants may be introduced into the semiconductorstructure 102 (e.g., into the region 104), e.g., through implantation orepitaxial growth. Then, microwave radiation may be used to anneal thesemiconductor structure 102 (e.g., the region 104) for dopantactivation, as shown in FIG. 1C. For example, the semiconductorstructure 102 (e.g., the region 104) may undergo solid-phase epitaxialre-growth in response to the microwave radiation. Themicrowave-radiation absorption of the semiconductor structure 102 may beincreased because of the large amount of defects generated during thePAI process. More dipoles related to the dopants may be formed in thesemiconductor structure 102 (e.g., in the region 104), and these dipolesmay vibrate and/or rotate in response to the applied microwaveradiation. The dipole formation and the dipole motions (e.g., vibrationand/or rotation) may eventually break down the bonds between the dopantsand the interstitial sites in the semiconductor structure 102 (e.g., inthe region 104), so that the dopants may be activated.

For example, the loss tangent of the semiconductor structure 102 may bein a range of about 0.5 to about 2. As an example, the dopants mayinclude phosphorous, phosphorous-based molecules (e.g., SiP, SiCP),germanium, germanium-based molecules (e.g., GeB, GeSnB, SiGeB), helium,boron, boron-based molecules, or a combination thereof. The dopantconcentration may be in a range from about 7×10²⁰/cm³ to 5×10²¹/cm³. Inone embodiment, the microwave radiation applied to the semiconductorstructure 102 may have a frequency in the range of about 2 GHz to about10 GHz. The semiconductor structure 102 may be pre-heated to atemperature in a range of 300° C. to 600° C. for the microwave-radiationannealing. The microwave radiation may be applied to the semiconductorstructure 102 for a time period within a range of about 40 seconds toabout 600 seconds.

A conductive layer (e.g., a metal silicide layer) may be formed (e.g.,through evaporation, sputtering, deposition) on the region 104, afterthe microwave-radiation annealing. Contacts for a semiconductor device(e.g., a transistor) may be formed based at least in part on theconductive layer, e.g., through rapid thermal processing or microwaveradiation annealing. The elements, the dosage and/or the energy of theimplantation species 108 may be adjusted to reduce the contactresistivity. For example, adding phosphorus-based materials to theimplantation species 108 may reduce the contact resistivity associatedwith a N-channel transistor formed in the semiconductor structure 102.

FIG. 2 depicts an example diagram for dopant activation using microwaveradiation. An microwave-absorption material 202 is placed at a distance(e.g., d) from the semiconductor structure 102 which includes dopants,where microwave radiation may be applied to both themicrowave-absorption material 202 and the semiconductor structure 102 inorder to activate the dopants in the semiconductor structure 102.

The microwave-absorption material 202 which has a large loss tangent mayabsorb sufficient microwave radiation and increase an electric fielddensity over the semiconductor structure 102. At the raised electricfield density, more and more dipoles related to the dopants may beformed in the semiconductor structure 102, and these dipoles may vibrateand/or rotate in response to the applied microwave radiation. Once theelectric field density over the semiconductor structure 102 exceeds athreshold, the dipole formation and the dipole motions (e.g., vibrationand/or rotation) may break down the bonds between the dopants and theinterstitial sites in the semiconductor structure 102 to activate thedopants. The distance between the microwave-absorption material 202 andthe semiconductor structure 102 may be adjusted to improve the dopantactivation.

For example, the microwave-absorption material 202 may includeboron-doped silicon germanium, silicon phosphide, titanium, nickel,silicon nitride, silicon dioxide, silicon carbide, or a combinationthereof. The microwave-absorption material 202 may have a much largersize than the semiconductor structure 102 so that the electric fielddensity may be approximately uniform over the semiconductor structure102.

In some embodiments, the semiconductor structure 102 may be placedbetween two microwave-absorption materials, where eachmicrowave-absorption material is at a predetermined distance from thesemiconductor structure 102. In certain embodiments, amicrowave-absorption layer may be formed on the semiconductor structure102, e.g., through epitaxial growth. The thickness of themicrowave-absorption layer may be adjusted to improve the dopantactivation. In one embodiment, multiple (e.g., two) microwave-absorptionlayers may be formed on different surfaces of the semiconductorstructure 102.

FIG. 3 depicts an example flow chart for dopant activation of asemiconductor structure using pre-amorphization implantation andmicrowave-radiation annealing. At 302, a substrate may be provided. At304, a semiconductor structure may be formed on the substrate. At 306,pre-amorphization implantation may be performed on the semiconductorstructure. At 308, microwave radiation may be applied to thesemiconductor structure to activate dopants in the semiconductorstructure for fabricating semiconductor devices. Microwave-radiationabsorption of the semiconductor structure is increased after thepre-amorphization implantation.

This written description uses examples to disclose the invention,include the best mode, and also to enable a person skilled in the art tomake and use the invention. The patentable scope of the invention mayinclude other examples that occur to those skilled in the art. Oneskilled in the relevant art will recognize that the various embodimentsmay be practiced without one or more of the specific details, or withother replacement and/or additional methods, materials, or components.Well-known structures, materials, or operations may not be shown ordescribed in detail to avoid obscuring aspects of various embodiments ofthe invention. Various embodiments shown in the figures are illustrativeexample representations and are not necessarily drawn to scale.Particular features, structures, materials, or characteristics may becombined in any suitable manner in one or more embodiments. Variousadditional layers and/or structures may be included and/or describedfeatures may be omitted in other embodiments. For example, a particularlayer described herein may include multiple components which are notnecessarily connected physically or electrically. Various operations maybe described as multiple discrete operations in turn, in a manner thatis most helpful in understanding the invention. However, the order ofdescription should not be construed as to imply that these operationsare necessarily order dependent. In particular, these operations neednot be performed in the order of presentation. Operations describedherein may be performed in a different order, in series or in parallel,than the described embodiment. Various additional operations may beperformed and/or described. Operations may be omitted in additionalembodiments.

This written description and the following claims may include terms,such as left, right, top, bottom, over, under, upper, lower, first,second, etc. that are used for descriptive purposes only and are not tobe construed as limiting. For example, terms designating relativevertical position may refer to a situation where a device side (oractive surface) of a substrate or integrated circuit is the “top”surface of that substrate; the substrate may actually be in anyorientation so that a “top” side of a substrate may be lower than the“bottom” side in a standard terrestrial frame of reference and may stillfall within the meaning of the term “top.” The term “on” as used herein(including in the claims) may not indicate that a first layer “on” asecond layer is directly on and in immediate contact with the secondlayer unless such is specifically stated; there may be a third layer orother structure between the first layer and the second layer on thefirst layer. The term “under” as used herein (including in the claims)may not indicate that a first layer “under” a second layer is directlyunder and in immediate contact with the second layer unless such isspecifically stated; there may be a third layer or other structurebetween the first layer and the second layer under the first layer. Theterm “substrate” may refer to any construction comprising one or moresemiconductive materials, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The embodiments of a device or article described herein canbe manufactured, used, or shipped in a number of positions andorientations. Persons skilled in the art will recognize variousequivalent combinations and substitutions for various components shownin the figures.

What is claimed is:
 1. A method for dopant activation in a semiconductorstructure for fabricating semiconductor devices, the method comprising:providing a substrate; forming a semiconductor structure on thesubstrate; performing pre-amorphization implantation on thesemiconductor structure; providing one or more microwave-absorptionmaterials capable of increasing an electric field density associatedwith the semiconductor structure; and applying microwave radiation tothe semiconductor structure and the microwave-absorption materials toactivate dopants in the semiconductor structure for fabricatingsemiconductor devices; wherein the microwave-absorption materials areconfigured to increase the electric field density in response to themicrowave radiation so as to increase the semiconductor structure'sabsorption of the microwave radiation.
 2. The method of claim 1, whereinthe pre-amorphization implantation is performed using a plasma dopingtechnique.
 3. The method of claim 1, wherein the pre-amorphizationimplantation is performed by injecting one or more implantation speciesinto the semiconductor structure.
 4. The method of claim 1, wherein theone or more implantation species include elements selected from a groupconsisting of: boron, phosphorus, arsenic, antinomy, germanium, silicon,helium, xenon, and argon.
 5. The method of claim 1, wherein apre-amorphization layer is formed in the semiconductor structure afterthe pre-amorphization implantation.
 6. The method of claim 5, whereinthe pre-amorphization layer includes an amorphous layer.
 7. The methodof claim 5, wherein the pre-amorphization layer includes defects.
 8. Themethod of claim 5, wherein the pre-amorphization layer has a thicknessin a range of approximately 5 nm to approximately 15 nm.
 9. The methodof claim 1, further comprising: forming a conductive layer on thesemiconductor structure to form one or more contacts for a semiconductordevice.
 10. The method of claim 9, wherein parameters related to thepre-amorphization implantation are adjusted to reduce a contactresistivity associated with the one or more contacts for thesemiconductor device.
 11. The method of claim 1, wherein a loss tangentof the semiconductor structure is in a range of approximately 0.5 toapproximately 2 after the pre-amorphization implantation.
 12. The methodof claim 1, wherein the microwave radiation has a frequency within arange of approximately 2 GHz to approximately 10 GHz.
 13. The method ofclaim 1, wherein the semiconductor structure is heated to a temperaturewithin a range of approximately 300° C. to approximately 600° C. whenthe microwave radiation is applied.
 14. The method of claim 1, whereinthe semiconductor structure is formed through epitaxial growth.
 15. Themethod of claim 1, wherein the microwave-absorption materials are placedat a distance from the semiconductor structure.
 16. The method of claim1, wherein the one or more microwave-absorption materials are formed onthe semiconductor structure.
 17. The method of claim 1, wherein themicrowave-absorption materials are selected from a group consisting of:boron-doped silicon germanium, silicon phosphide, titanium, nickel,silicon nitride, silicon dioxide, and silicon carbide.
 18. An articlefor fabricating semiconductor devices, comprising: a substrate; asemiconductor structure formed on the substrate; a pre-amorphizationlayer formed in the semiconductor structure through pre-amorphizationimplantation, microwave-radiation absorption of the semiconductorstructure being increased after the pre-amorphization implantation; anda microwave-absorption material layer placed at a predetermined distancefrom the semiconductor structure, the microwave-absorption materiallayer being configured to increase an electric field density associatewith the semiconductor structure in response to microwave radiation,wherein dopants in the semiconductor structure are activated by applyingmicrowave radiation to the semiconductor structure.
 19. The article ofclaim 18, wherein the pre-amorphization layer includes an amorphouslayer.